Heat-seal package and method of packaging

ABSTRACT

According to the present invention, in overwrapping an object to be packaged, the object is wrapped with a packaging material in such a manner as to form a tubular shape, which packaging material is heat-sealable on both sides thereof and, as required, has heat shrinkability or gas-barrier properties; the overlap portion of the packaging material is heat-sealed in a lap seal fashion: and an opening portion formed at each end of the lap seal line is heat-sealed. The lap-heat-sealed portion of the package thus obtained has a satisfactory strength with liquid leakage prevented, and the unevenness of this portion is inconspicuous. Further, respective sealed portions at both ends of the package exhibit a good appearance because of the absence of a folded portion. The resulting package is excellent in seal strength and appearance and hence highly valuable on a commercial basis. Further, where the packaging material is self-tacky and, at the same time, heat-sealable within the temperature range for heat shrinkage, exposing the package provisionally sealed by self-tackiness to a heating environment for heat shrinkage will give a package with heat sealing completely achieved during the heat shrink treatment without the need of an additional heat-sealing process for the provisionally-sealed portion.

TECHNICAL FIELD

The present invention relates to a method for overwrap-packaging anarticle using a packaging material which is heat-sealable on both sidesthereof and to a resulting package. In particular, where the packagingmaterial is both self-tacky and heat-shrinkable, the packaging materialis provisionally sealed by virtue of its self-tackiness, then subjectedto a heating environment for heat shrinkage, thereby obtaining a packagewith its provisionally-sealed portion completely heat-sealed by the heatshrink treatment without the need of an additional heat-sealingtreatment.

BACKGROUND ART

Hitherto, various methods have been proposed and practically employedfor overwrap-packaging an object with a plastic film.

For instance, packaging methods of the type which seals three sides of apackage include one adapted to heat-seal all the three sides of apackage by melt-cut sealing or band sealing (heat-sealing using aheating bar, heating continuous belt or heating disk edge to form aband-like sealed portion), one adapted to fin-heat-seal one of the threesides of a package and to melt-cut-seal or band-seal the two remainingsides thereof, and one adapted to electrostatic-seal one side of apackage in a lap seal fashion and to melt-cut-seal or band-seal the tworemaining sides thereof.

In addition, there is known a packaging method using a stretched filmwherein one side of a package is lap-heat-sealed and the two remainingsides thereof are folded onto the bottom surface of the package andfixed thereto by heat sealing.

Such conventional methods, however, involve a problem that wherepackages each having a heat-sealed portion resulting from melt-cutsealing on the bottom surface thereof are transported or displayed in astacked fashion, the melt-cut-sealed portion on the bottom surface of anupper package is brought into close contact with the top surface of theunderlying package and rubbed thereby due to vibration or the like andis hence prone to rupture.

Although rupture of such kind is hard to occur if a package isfin-heat-sealed on the bottom surface thereof, another problem arisesthat since the fin-heat-sealed portion of the package is considerablythick and forms a projection on the bottom surface of the package,stacking this package on an object having, for example, a soft surfacewould frequently leave a mark of the sealed portion on the top surfaceof the underlying object.

With the package which is electrostatic-sealed on the bottom surfacethereof in a lap seal fashion, the problem of the aforementioned markingwill not arise because the sealed portion is thin and does not projectso much. However, such a package suffers a problem that the sealedportion is likely to be unsealed since it is not fusion-bonded and aproblem that if the package contains a liquid such as water or juice,such a liquid is easy to leak from the package. Further, in this caseanother problem is present that since the packaging material must be anelectrostatically chargeable film, such a film is easy to collect dustdue to static electricity and is inevitably poor in antifog properties.

Further, with the package using a stretched film wherein one side of thepackage is lap-heat-sealed and the two remaining sides thereof arefolded onto the bottom surface of the package and fixed thereto by heatsealing, there is a drawback that the portions folded onto the bottomsurface of the package are wrinkled and, hence, openings are left in thewrinkled portion to frequently permit a liquid to leak therethrough. Inaddition such a wrinkled portion degrades the appearance of the package.

DISCLOSURE OF THE INVENTION

The present invention has been attained as a result of intensive effortsto solve the foregoing various problems. According to the presentinvention, such problems are all solved by wrapping an object with apackaging material such as a wrapping film, forming an overlap portionof the packaging material on any one surface, for example, bottomsurface, of the object, lap-heat-sealing the overlap portion andheat-sealing opening portions formed on opposite ends of thelap-heat-sealed portion.

Thus, the present invention is directed to a method for packaging anobject which is employed in overwrapping the object, characterized by:covering the object with a packaging material in such a manner as towrap the packaging material around the object, the packaging materialbeing heat-sealable on both sides thereof; lap-heat-sealing the overlapportion of the packaging material; and sealing opening portionsrespectively formed at opposite ends of the lap-heat-seal line by heatsealing. The present invention is also directed to a package resultingfrom the above method.

The present invention uses as the packaging material a film which isheat-sealable on both sides thereof. More preferably, such a film isself-tacky at its surface, heat-shrinkable, or both stretchable andheat-shrinkable. The packaging material typically exhibitsself-tackiness when surfaces thereof are brought into mutual and closecontact with each other.

The film may be a single-layered film but preferably a multilayered filmcomprising a core layer and a sealant layer having heat-sealability oneach side of the core layer. A film for the core layer may be impartedwith gas barrier property, good modulas of elasticity, or otherpreferable characteristics suitable for the purpose of individualpackage. Examples of the film material forming each layer includepolyolefin resins, vinyl chloride resins, polyamide resins andethylene-vinyl alcohol resins. Nevertheless, any other materials may beused without particular limitations as far as they meet theabove-mentioned requirements.

To be described next is a method for producing a package using theaforementioned packaging material according to the present invention.

An object to be packaged is wrapped with the aforementioned packagingmaterial in such a manner as to form a tubular shape, followed by heatsealing of the overlapped ends of the packaging material by applying aheating bar heated to such a temperature as to allow heat sealing of thepackaging material or by placing the overlapped ends onto a hot plate.The peripheral edge of each opening portion formed at each end of thetubular shape is flatly collapsed and then heat-sealed by melt-cutsealing, band sealing or the like.

In this case if the packaging material to be used has self-tackiness,the overlap portion and the opening portions at opposite ends which areformed when the object is tubularly wrapped with the packaging materialare provisionally sealed by merely compressing the same. Hence, suchprovisionally-sealed portions will not be unsealed or shifted easily.This allows those opening portions to be heat-sealed directly or theoverlap portion on the bottom surface of the package to be sealeddirectly by means of a hot plate or the like.

Alternatively, if the packaging material to be used has heatshrinkability, after heat-sealing the three portions, i.e. the overlapportion and the opening portions, the packaging film is made to shrinkby allowing the package to pass through a heating furnace or to beexposed to hot air or hot water, whereby a package with tight appearancecan be obtained.

Further, where the packaging material to be used is self-tacky,heat-sealable and heat-shrinkable and at the same time the heat-seallayer is heat-sealable within a temperature range suitable for heatshrinkage, the overlap portion on the bottom surface of the package andthe opening portions at opposite ends are collapsed to achieveprovisional sealing, and then the package is directly subjected to theheat shrink treatment without any particular heat-sealing process,thereby obtaining a shrink package with the packaging materialcompletely heat-sealed while heat-shrinked during the heat shrinktreatment.

If desired, suitable unsealability can be imparted to the package byproviding the packaging material with a V-shaped notch or a cut line ofperforations in a portion thereof contacting the object or in a portionthereof between each opening portion sealed and the object.

SUMMARY OF DRAWINGS

FIG. 1 is a partial sectional view showing an example of the packagingmaterial used in the present invention.

FIGS. 2-4 are perspective views showing an example of the packagingmethod of the present invention (hereinafter referred to as "Method 1")in order of steps.

FIG. 5 is another example of the packaging method of the presentinvention.

FIG. 6 is a further example of the packaging method of the presentinvention wherein a heat-shrinkable film is used as the packagingmaterial 1.

FIG. 7 is a still further example of the packaging method of the presentinvention wherein a heat-shrinkable film is used as the packagingmaterial 1.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described more specifically by way ofexamples thereof.

Reference to FIG. 1 illustrates a packaging material 1 that is athree-layer film comprising a core layer 2 and a self-tacky,heat-sealable layer 3 laminated on each side of the core layer 2.

As shown in FIG. 2, the packaging material 1 is wrapped around an object10 to be packaged to form a tubular shape including an overlap portion11 of the packaging material 1 in lap seal fashion and an openingportion 12 at each end of the overlap portion 11.

The overlapped ends of the packaging material 1 in the overlap portion11 in lap seal fashion are stuck to each other by the self-tackiness ofthe packaging material 1 to provide provisional-sealing of the overlapportion 11. The opening portion 12 is pressed from above and from belowto be provisionally-sealed by the self-tackiness of the packagingmaterial 1.

Thus, there is obtained a provisional package as shown in FIG. 3. InFIG. 3, hatched areas 13 and 14 are the thus provisionally-sealedportions.

Then, as shown in FIG. 4, a cut line 15 of perforations is provided tothe packaging material 1 by applying thereto a rotary perforation cutterat a location between each provisionally-sealed portion 14 and theobject 10. The wrapped object is placed on a hot plate to allow secureheat-sealing of the provisionally-sealed portion 13 of the overlapportion 11 in lap seal fashion and the provisionally-sealed portion 14of the opening portion 12 is securely heat-sealed by using a bar sealer,thus yielding a final package. In FIG. 4, a cross-hatched area 16 and across-hatched area 17 are the thus heat-sealed portions.

In the method exemplified by FIG. 5, the provisionally-sealed portion 14of the opening portion 12 shown in FIG. 3 is securely melt-cut-sealed.The melt-cut-sealed portion is indicated by numeral 18. The treatment ofthe provisionally-sealed portion 13 is the same as in Method 1.

In the method exemplified by FIG. 6, the provisional package shown inFIG. 3 is passed through a shrink tunnel so that the packaging material1 is shrunk and the provisionally-sealed portions 13 and 14 are securelyheat-sealed by the heat of the shrink tunnel to give a final package. InFIG. 6, the cross-hatched area 19 is the portion heat-sealed by the heatof the shrink tunnel.

In the method exemplified by FIG. 7, a cut-line 15 of the perforationsis provided in the provisional package shown in FIG. 3 and theprovisionally-sealed portion 14 is melt-cut-sealed. The resultantarticle is then passed through a shrink tunnel to give a final package.In FIG. 7, the melt-cut-sealed portion is indicated by numeral 20 andthe cross-hatched area 21 is the portion heat-sealed by the heat of theshrink tunnel.

EXAMPLE 1

As a packaging material there was used a stretchable, heat-shrinkable,polyolefin-based, multilayered film having a width of 25 cm and athickness of 13 μ (KOHJINKORAP, a product of Kohjin Co., Ltd.), the heatshrinkage percentage of the film being 40% in both longitudinal andtransverse directions at 100° C. The film was wrapped around apolypropylene tray having a length of 10 cm in the longitudinaldirection, a length of 18 cm in the transverse direction and a height of1.5 cm, on which 160 g of pickles were placed, as an object to bepackaged, in the transverse direction of the tray. The film was then cutto have an overlap portion having a width of about 30 mm and extendingcentrally of the bottom surface of the tray. The resulting wrappedobject was placed upon a hot plate at 100° C. for one second to allowheat sealing of the overall area of the overlap portion in a lap heatseal fashion. In turn, an opening portion formed at each end of the lapheat sealed portion was collapsed, then heat-sealed at a locationadjacent art end of the tray by melt-cut sealing using a knife of 1.5mmR at 180° C.

The resulting package was heated for two seconds by passing it through ahot-air tunnel heated at 110° C. to give a shrink package.

Packages of the type thus obtained were stacked one upon another up tosix stages within a cardboard box, then subjected to a vibration testfor 40 minutes by placing the box on a flat board adapted to reciprocate50 times per minute at an amplitude of 20 cm. As a result, thelap-heat-sealed area on the bottom surface of each of the packages wasfound to be uniformly transparent and smooth with no rupture of seal.Further, the melt-cut-sealed portion of each selvage exhibited aclear-cut appearance, and the package did not permit the juice ofpickles to leak therefrom no matter how inclined. The shrink packagethus obtained was a commercial package which was excellent inappearance, strength and liquid-tight property.

EXAMPLE 2

As a packaging material there was used an ethylene-vinyl alcohol-basedmultilayered film of barrier properties having a width of 27 cm and athickness of 14 μm, the film comprising a 2 μm-thick EVOH film layer anda 6 μm-thick polyethylene film layer laminated on each side of the EVOHfilm layer. The film was wrapped around a polypropylene tray having alength of 12 cm in the longitudinal direction, a length of 20 cm in thetransverse direction and a height of 2.0 cm, on which 200 g of chilledhamburger was placed, as an object to be packaged, in the transversedirection of the tray. The film was then cut to have an overlap portionhaving a width of about 20 mm and extending centrally of the bottomsurface of the tray. The resulting wrapped object was directly placedupon a hot plate at 100° C. for two seconds to allow heat-sealing of theoverall area of the overlap portion in a lap heat seal fashion. In turn,an opening portion formed at each end of the lap-heat-sealed portion waspressed to be collapsed, then heat-sealed at a location adjacent an endof the tray using a 5 mm-wide bar sealer heated at 110° C.

The package thus obtained was subjected to the same test as in Example 1for 40 minutes. As a result, the lap-heat-sealed area on the bottomsurface of the package was found to be uniformly transparent and smoothwith no rupture of seal. Further, the bar-sealed portion in each selvageportion was found to be sealed securely. Consequently, the package thusobtained was a commercial package which was excellent in appearance,strength and barrier properties.

EXAMPLE 3

As a packaging material there was used a stretchable, heat-shrinkable,polyethylene-based, multilayered film, the film comprising a 10.4μm-thick core layer formed of a linear low-density polyethylene resinhaving a melting point of 126° C. (a main peak by DSC measurement ) anda heat shrinkage initiating temperature of 80° C. and, laminated on eachside of the core layer, a 1.3 μm-thick, self-tacky, heat-sealable layerformed of a mixture of 49% by weight of a linear low-densitypolyethylene resin having a melting point of 80° C. (the same as theabove), 49% by weight of the linear low-density polyethylene resin asused in the core layer and 2% by weight of a tackifier (ARKON P115, aproduct of Arakawa Chemical Co.), the heat-seal initiating temperatureof the heat-seal layer being 70° C. The film was wrapped around a lunchbox of polypropylene filled with a variety of lunch foods (MakunouchiBento), as an object to be packaged, in the transverse direction of thelunch box. The film was cut to have an overlap portion of 15 mm in widthon the bottom surface of the lunch box. The overlapped ends of thewrapping film were stuck to each other by the self-tackiness of thefilm. In turn, a tubular opening portion formed at each end of the boxwas pressed from above and from below to be closed by self-tackiness ofthe film, thereby obtaining a provisional package. A cut line ofperforations was then provided to the packaging material by applyingthereto a rotary perforation cutter at a location spaced by 5 mm fromthe lunch box between each dosed end of the packaging material and thelunch box. The thus obtained provisional package was passed through a100° C. hot air shrink tunnel for two seconds. The resulting package wasa complete package with its provisionally sealed portions at the bottomsurface and opposite ends thereof being securely heat-sealed by the heatof the shrink tunnel.

The thus obtained package was subjected to a vibration test for 40minutes in the same manner as in Example 1. As a result, the package wasfound to have the overlap portion and closed end portions securelysealed with no rupture of seal.

When this package was held by hands and the opposite end portionsthereof were pulled outwardly by hands, the packaging material was cuteasily along the cut line of perforations to allow removal of the lunchbox with ease.

COMPARATIVE EXAMPLE 1

Using a packaging material and an object to be packaged which werecompletely identical with those used in Example 1, the film was wrappedaround the tray in the transverse direction of the tray and the film washeat-sealed by melt-cut sealing so as to have a seal line extendingcentrally of the bottom surface of the tray. In turn, an opening portionformed at each end of the tray by the heat-sealing on the bottom wascollapsed, then heat-sealed at a portion adjacent an end of the tray bymelt-cut sealing.

The resulting package was heated for six seconds by passing it through ahot-air tunnel heated at 120° C. to give a shrink package.

Packages of the type thus obtained were stacked one upon another up tosix stages within a cardboard box, then subjected to a vibration testfor 40 minutes by placing the box on a flat board adapted to reciprocate50 time per minute. As a result, some packages were each found to have apinhole-like rupture in a portion of the heat-sealed portion in thebottom surface of the package because of friction with the top surfaceof the underlying package due to vibration. When these packages wereinclined at various angles, juice was found to ooze from the pinhole.

The shrink package thus obtained was one which was incomplete instrength and in liquid-tight properties.

COMPARATIVE EXAMPLE 2

As a packaging material there was used an electrostatic-chargeable,heat-shrinkable, polypropylene-based film of 28 cm in width and 15 μthickness (KOHJINPOLYSET, a product of Kohjin Co., Ltd.). The film waswrapped around a polypropylene tray having a length of 10 cm in thelongitudinal direction, a length of 18 cm in the transverse directionand a height of 1.5 cm, on which 160 g of pickles were placed, as anobject to be packaged, in the transverse direction of the tray. The filmwas cut to have an overlap portion having a width of about 30 mm andextending centrally of the bottom surface of the tray. The overall areaof the overlap portion on the bottom was allowed to beelectrostatic-sealed in a lap seal fashion. In turn, an opening portionformed at each end of the electrostatic-lap-sealed area was collapsed,then heat-sealed at a location adjacent an end of the tray by melt-cutsealing.

The resulting package was heated for six seconds by passing it through ahot-air tunnel heated at 160° C. to give a shrink package.

Packages of the type thus obtained were stacked one upon another up tosix stages within a cardboard box, then subjected to a vibration testfor 40 minutes by placing the box on a flat board adapted to reciprocate50 times per minute at an amplitude of 20 cm. As a result, theelectrostatic-lap-sealed area on the bottom surface of some packages wasfound to have some exfoliation though seemed to be transparent andsmooth. Variously inclining these packages resulted in ooze of juice ofpickles therefrom.

The thus obtained shrink package was one which had a problem ofsealability and liquid-tight properties at the electrostatic-sealedportion on the bottom surface thereof.

COMPARATIVE EXAMPLE 3

In a manner similar to that of Example 1 except that the packagingmaterial was 34 cm wide, a tubularly wrapped object was given as havinga lap-heat-sealed portion on the bottom surface thereof. An openingportion formed at each end of the heat-sealed area was collapsed andfolded onto the bottom surface. The wrapped object with its packagingmaterial thus folded was placed upon a hot plate heated at 100° C. tofix the folded portions to the bottom surface of the package by fusionbonding, thereby achieving sealing.

The package thus obtained was found to have a bottom surface exhibitingnot so good appearance. Further, variously inclining this packageresulted in ooze of juice of the packaged object from the folded andfixed portion on the bottom surface thereof. This package when displayedas a commercial article had a degraded value on a commercial basis dueto its appearance.

INDUSTRIAL APPLICABILITY

According to the present invention, in overwrapping an object to bepackaged, the object is wrapped with a packaging material in such amanner as to form a tubular shape, which packaging material isheat-sealable on both sides thereof and, as required, has heatshrinkability or gas-barrier properties; the overlap portion of thepackaging material is heat-sealed in a lap seal fashion; and an openingportion formed at each end of the lap seal line is heat-sealed. Thelap-heat-sealed portion of the package thus obtained has a satisfactorystrength with liquid leakage prevented, and the unevenness of thisportion is inconspicuous. Further, respective sealed portions at bothends of the package exhibit a good appearance because of the absence ofa folded portion. The resulting package is excellent in seal strengthand appearance and hence highly valuable on a commercial basis. Further,where the packaging material is self-tacky and, at the same time,heat-sealable within the temperature range for heat shrinkage, exposingthe package provisionally sealed by self-tackiness to a heatingenvironment for heat shrinkage will give a package with heat sealingcompletely achieved during the heat shrink treatment without the need ofan additional heat-sealing process for the provisionally-sealed portion.

I claim:
 1. A method for packaging an object which is employed inoverwrapping the object, comprising: wrapping a sheet of packagingmaterial around an object to form a tubular shape, wherein the sheet ofpackaging material provides both self-tackiness and heat-sealability oneach side thereof; pressing an overlap portion of said sheet ofpackaging material in a lap seal fashion and an opening portion at eachend of the overlap portion to provisionally seal these portions by theself-tackiness thereof, thereby giving a provisional package; andheat-sealing the provisionally-sealed portions.
 2. The method of claim1, wherein said sheet of packaging material is stretchable.
 3. Themethod of claim 1, wherein the sheet of packaging material is amulti-layer film.
 4. The method of claim 1, wherein theprovisionally-sealed opposite ends of the overlap portion are sealed bymelt-cut sealing.
 5. The method of claim 1, which further comprisesafter obtaining the provisional package, providing a line ofperforations in a portion of the sheet of packaging material between aportion where the sheet of packaging material contacts the object and atleast one of the provisionally-sealed portions at opposite ends of theoverlap portion.
 6. A method for packaging an object which is employedin overwrapping the object, comprising: wrapping a sheet of packagingmaterial around an object to form a tubular shape, wherein said sheet ofpackaging material is heat-shrinkable and provides self-tackiness andheat-sealability on each side thereof, the heat-sealability beingprovides within a temperature range suited for heat shrinkage of saidsheet of packaging material; pressing an overlap portion of the sheet ofpackaging material in a lap seal fashion and an opening portion formedat each end of the overlap portion to provisionally seal these portionsby the self-tackiness thereof, thereby giving a provisional package; andsubjecting said provisional package to a heat shrink treatment underheat shrink conditions of the sheet of packaging material while at thesame time heat-sealing the portions of the provisional package whichhave been provisionally-sealed by the self-tackiness thereof.
 7. Themethod of claim 6, wherein the sheet of packaging material isstretchable.
 8. The method of claim 6, wherein the sheet of packagingmaterial is a multi-layer film.
 9. The method of claim 6, which furthercomprises after obtaining the provisional package and prior to the heatshrink treatment, providing a line of perforations in a portion of thesheet of packaging material between a portion where the sheet ofpackaging material contacts the object and at least one of theprovisionally-sealed portions at opposite ends of the overlap portion.10. A package comprising an object packaged with a sheet of packagingmaterial which provides self-tackiness and heat-sealability on each sidethereof, the package obtained by wrapping the sheet of packagingmaterial around the object to form a tubular shape; pressing an overlapportion of the sheet of packaging material in lap seal fashion and anopening portion at each end of the overlap portion to provisionally sealthese portions by the self-tackiness thereof, thereby giving aprovisional package; and heat-sealing the provisionally-sealed portions.11. The package of claim 10, wherein the sheet of packaging material isstretchable.
 12. The package of claim 10, wherein the sheet of packagingmaterial is a multi-layer film.
 13. The package of claim 10, wherein theprovisionally-sealed opposite ends of the overlap portion are sealed bymelt-cut sealing.
 14. The package of claim 10, which further comprisesafter obtaining the provisional package, providing a line ofperforations in a portion of the sheet of packaging material between aportion where the sheet of packaging material contacts the object and atleast one of the provisionally-sealed portions at opposite ends of theoverlap portion.
 15. A package comprising an object packaged with asheet of packaging material which is heat-shrinkable and which providesself-tackiness and heat-sealability on each side thereof, theheat-sealability being provided within a temperature range suited forheat shrinkage of the packaging material, the package obtained bywrapping the sheet of packaging material around the object to form atubular shape; pressing an overlap portion of the sheet of packagingmaterial in a lap seal fashion and an opening portion formed at each endof the overlap portion to seal these portions provisionally by theself-tackiness thereof, thereby giving a provisional package; andsubjecting the provisional package to a heat shrink treatment under heatshrink conditions of the sheet of packaging material while at the sametime heat-sealing the portions of the provisional package which havebeen provisionally-sealed by the self-tackiness thereof.
 16. The packageof claim 15, wherein the sheet of packaging material is stretchable. 17.The package of claim 15, wherein the sheet of packaging material is amulti-layer film.
 18. The package of claim 15, which further comprisesafter obtaining the provisional package and prior to the heat shrinktreatment, providing a line of perforations in a portion of the sheet ofpackaging material between a portion where the sheet of packagingmaterial contacts the object and at least one of theprovisionally-sealed portions at opposite ends of the overlap portion.